The horizontal first is not for tight, tight lays with big saws with awkward, wet footing, IME.
You can get away with lots with small and medium saws.
You can get away with a lot in good cutting conditions.
If you have 15-20* to lay the trunk into, sure you can shoot from the hip/ shoulder-up. When I've got a tight lay, I use the gunning sights like a sniper, no wishful gunning looking from above.
If you're a pro Feller, you're good to go, either way. You're a pro feller. You can also slam in all your cuts from either side, conventional or Humboldt.
Idk, steep ground, wet, mossy, slippery flares, I'm not going to risk pulling that big saw down on top of me while trying to line up, looking from above.
Slam those dogs in, get the saw weight on the tree.
If you have to cut high on the trunk, same thing,
and a conventional is going to be harder to cut, remove the face cut chunk, clean up if needed.
I think conventional could be renamed the ax-chopper way.
Ymmv